I like this idea, especially weather effects/impacts. If they decide to add a stealth system, which I think they will considering they want to have tactical combat, I think it would be appropriate if weather plays a role in how stealth works. For example, it should be easier to pick off sentries on a dark and rainy night rather than, say, broad daylight. Generally, just sneaking about should be easier at night than day.
And while we're on the subject, it would be neat if thunder had some funtion, like, you can shoot a sentry without the risk of their garbled last cries reaching out to their friends.